1. Field of the Invention
The present invention relates to a leaktight seal for a circular vane stage and in particular a stage for "hammer legged" vanes, i.e. vanes being fastened to a disc using a leg with a bulbous cross-section that is inserted into a circular throat provided in a peripheral surface of the disc.
2. Description of the Related Art
If we refer to FIG. 1, vanes 1 of this kind can be seen on the circumference of discs 2 of a gas turbine stator 3 where they alternate with immobile vanes 4 used to rectify a gas flow and that are fastened to a stator 5. The vanes 1 comprise a blade 6 that constitutes the active section of the vanes and that lies in a gas flow chamber 7, a platform 8 used to define chamber 7 and that is adjacent to blade 6, a leg 9 that is inserted into a circular throat 10 of the relevant disc 2 and a fastener 11 that connects leg 9 to platform 8 and that passes through a collar 12 of throat 10 to reach the outside. The leg 9 has a bulbous cross-section, in other words, it widens from the zone at fastener 11 and given that collar 12 is narrower than the leg, said leg 9 is maintained in throat 10 despite the centrifugal forces. Disc 2 is, however, provided with a hole at a specific point on its circumference that widens collar 12 to enable legs 9 of vanes 1 to be inserted successively in throat 10 through said hole before vanes 1 are slid around disc 2 to reach their definitive position.
Re-circulated air may be noticed under platforms 8, in other words, air that is returned upstream towards the compressors in the machine and the low pressures, in the opposite direction to the flow of gas in chamber 7. This re-circulated air travels between vane 1 and disc 2 through throat 10 despite the parts being adjustable in this zone. This re-circulation leads to performance loss of the machine. Various kinds of leaktight seals have been put forward in order to reduce the performance loss such as circular Inconel wires 14 that are housed in throats 15 with a small cross-section cut into a peripheral surface 16 of disc 2, said wires 14 being under platforms 8 next to legs 9. The drawback with this solution is that the centrifugal forces cause wires 14 to leave throats 15 and move upwards to platforms 8 where they become worn or even cut. A leaktight seal that does not cause this damage to the vanes 1 is therefore preferred, particularly given that vanes 1, that are generally titanium, are expensive and also that the loss of a piece of a platform 8 can lead to serious damage to the compressor.